The ternary V-VI-VII chalcohalides consist of one cation and two anions. Trivalent antimony - with a distinctive 5s2 electronic configuration - can be combined with a chalcogen (e.g., S or Se) and halide (e.g., Br or I) to produce photoactive ferroelectric semiconductors with similarities to the Pb halide perovskites. We report - from relativistic quasi-particle self-consistent GW theory - that these materials have a multi-valley electronic structure with several electron and hole basins close to the band extrema. We predict ionisation potentials of 5.3-5.8 eV from first-principles for the three materials, and assess electrical contacts that will be suitable for achieving photovoltaic action from these unconventional compounds.
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